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<a name="boost.numeric.odeint.runge_kutta4"></a><div class="titlepage"></div>
<div class="refnamediv">
<h2><span class="refentrytitle">Class template runge_kutta4</span></h2>
<p>boost::numeric::odeint::runge_kutta4 — The classical Runge-Kutta stepper of fourth order. </p>
</div>
<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="../../../header/boost/numeric/odeint/stepper/runge_kutta4_hpp.html" title="Header &lt;boost/numeric/odeint/stepper/runge_kutta4.hpp&gt;">boost/numeric/odeint/stepper/runge_kutta4.hpp</a>&gt;

</span><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> State<span class="special">,</span> <span class="keyword">typename</span> Value <span class="special">=</span> <span class="keyword">double</span><span class="special">,</span> <span class="keyword">typename</span> Deriv <span class="special">=</span> <span class="identifier">State</span><span class="special">,</span> 
         <span class="keyword">typename</span> Time <span class="special">=</span> <span class="identifier">Value</span><span class="special">,</span> 
         <span class="keyword">typename</span> Algebra <span class="special">=</span> <span class="keyword">typename</span> <span class="identifier">algebra_dispatcher</span><span class="special">&lt;</span> <span class="identifier">State</span> <span class="special">&gt;</span><span class="special">::</span><span class="identifier">algebra_type</span><span class="special">,</span> 
         <span class="keyword">typename</span> Operations <span class="special">=</span> <span class="keyword">typename</span> <span class="identifier">operations_dispatcher</span><span class="special">&lt;</span> <span class="identifier">State</span> <span class="special">&gt;</span><span class="special">::</span><span class="identifier">operations_type</span><span class="special">,</span> 
         <span class="keyword">typename</span> Resizer <span class="special">=</span> <span class="identifier">initially_resizer</span><span class="special">&gt;</span> 
<span class="keyword">class</span> <a class="link" href="runge_kutta4.html" title="Class template runge_kutta4">runge_kutta4</a> <span class="special">:</span> <span class="keyword">public</span> boost::numeric::odeint::explicit_generic_rk&lt; StageCount, Order, State, Value, Deriv, Time, Algebra, Operations, Resizer &gt;
<span class="special">{</span>
<span class="keyword">public</span><span class="special">:</span>
  <span class="comment">// types</span>
  <span class="keyword">typedef</span> <span class="identifier">stepper_base_type</span><span class="special">::</span><span class="identifier">state_type</span>      <a name="boost.numeric.odeint.runge_kutta4.state_type"></a><span class="identifier">state_type</span><span class="special">;</span>     
  <span class="keyword">typedef</span> <span class="identifier">stepper_base_type</span><span class="special">::</span><span class="identifier">value_type</span>      <a name="boost.numeric.odeint.runge_kutta4.value_type"></a><span class="identifier">value_type</span><span class="special">;</span>     
  <span class="keyword">typedef</span> <span class="identifier">stepper_base_type</span><span class="special">::</span><span class="identifier">deriv_type</span>      <a name="boost.numeric.odeint.runge_kutta4.deriv_type"></a><span class="identifier">deriv_type</span><span class="special">;</span>     
  <span class="keyword">typedef</span> <span class="identifier">stepper_base_type</span><span class="special">::</span><span class="identifier">time_type</span>       <a name="boost.numeric.odeint.runge_kutta4.time_type"></a><span class="identifier">time_type</span><span class="special">;</span>      
  <span class="keyword">typedef</span> <span class="identifier">stepper_base_type</span><span class="special">::</span><span class="identifier">algebra_type</span>    <a name="boost.numeric.odeint.runge_kutta4.algebra_type"></a><span class="identifier">algebra_type</span><span class="special">;</span>   
  <span class="keyword">typedef</span> <span class="identifier">stepper_base_type</span><span class="special">::</span><span class="identifier">operations_type</span> <a name="boost.numeric.odeint.runge_kutta4.operations_type"></a><span class="identifier">operations_type</span><span class="special">;</span>
  <span class="keyword">typedef</span> <span class="identifier">stepper_base_type</span><span class="special">::</span><span class="identifier">resizer_type</span>    <a name="boost.numeric.odeint.runge_kutta4.resizer_type"></a><span class="identifier">resizer_type</span><span class="special">;</span>   

  <span class="comment">// <a class="link" href="runge_kutta4.html#boost.numeric.odeint.runge_kutta4construct-copy-destruct">construct/copy/destruct</a></span>
  <a class="link" href="runge_kutta4.html#idm29434-bb"><span class="identifier">runge_kutta4</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">algebra_type</span> <span class="special">&amp;</span> <span class="special">=</span> <span class="identifier">algebra_type</span><span class="special">(</span><span class="special">)</span><span class="special">)</span><span class="special">;</span>

  <span class="comment">// <a class="link" href="runge_kutta4.html#idm29382-bb">public member functions</a></span>
  <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> System<span class="special">,</span> <span class="keyword">typename</span> StateIn<span class="special">,</span> <span class="keyword">typename</span> DerivIn<span class="special">,</span> 
           <span class="keyword">typename</span> StateOut<span class="special">&gt;</span> 
    <span class="keyword">void</span> <a class="link" href="runge_kutta4.html#idm29383-bb"><span class="identifier">do_step_impl</span></a><span class="special">(</span><span class="identifier">System</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">StateIn</span> <span class="special">&amp;</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">DerivIn</span> <span class="special">&amp;</span><span class="special">,</span> <span class="identifier">time_type</span><span class="special">,</span> 
                      <span class="identifier">StateOut</span> <span class="special">&amp;</span><span class="special">,</span> <span class="identifier">time_type</span><span class="special">)</span><span class="special">;</span>
  <span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> StateIn<span class="special">&gt;</span> <span class="keyword">void</span> <a class="link" href="runge_kutta4.html#idm29423-bb"><span class="identifier">adjust_size</span></a><span class="special">(</span><span class="keyword">const</span> <span class="identifier">StateIn</span> <span class="special">&amp;</span><span class="special">)</span><span class="special">;</span>
<span class="special">}</span><span class="special">;</span></pre></div>
<div class="refsect1">
<a name="idm47793"></a><h2>Description</h2>
<p>The Runge-Kutta method of fourth order is one standard method for solving ordinary differential equations and is widely used, see also <a href="http://en.wikipedia.org/wiki/Runge%E2%80%93Kutta_methods" target="_top">en.wikipedia.org/wiki/Runge-Kutta_methods</a> The method is explicit and fulfills the Stepper concept. Step size control or continuous output are not provided.</p>
<p>This class derives from explicit_stepper_base and inherits its interface via CRTP (current recurring template pattern). Furthermore, it derivs from <a class="link" href="explicit_generic_rk.html" title="Class template explicit_generic_rk">explicit_generic_rk</a> which is a generic Runge-Kutta algorithm. For more details see explicit_stepper_base and <a class="link" href="explicit_generic_rk.html" title="Class template explicit_generic_rk">explicit_generic_rk</a>.</p>
<p>
</p>
<div class="refsect2">
<a name="idm47801"></a><h3>Template Parameters</h3>
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">
<pre class="literallayout"><span class="keyword">typename</span> State</pre>
<p>The state type. </p>
</li>
<li class="listitem">
<pre class="literallayout"><span class="keyword">typename</span> Value <span class="special">=</span> <span class="keyword">double</span></pre>
<p>The value type. </p>
</li>
<li class="listitem">
<pre class="literallayout"><span class="keyword">typename</span> Deriv <span class="special">=</span> <span class="identifier">State</span></pre>
<p>The type representing the time derivative of the state. </p>
</li>
<li class="listitem">
<pre class="literallayout"><span class="keyword">typename</span> Time <span class="special">=</span> <span class="identifier">Value</span></pre>
<p>The time representing the independent variable - the time. </p>
</li>
<li class="listitem">
<pre class="literallayout"><span class="keyword">typename</span> Algebra <span class="special">=</span> <span class="keyword">typename</span> <span class="identifier">algebra_dispatcher</span><span class="special">&lt;</span> <span class="identifier">State</span> <span class="special">&gt;</span><span class="special">::</span><span class="identifier">algebra_type</span></pre>
<p>The algebra type. </p>
</li>
<li class="listitem">
<pre class="literallayout"><span class="keyword">typename</span> Operations <span class="special">=</span> <span class="keyword">typename</span> <span class="identifier">operations_dispatcher</span><span class="special">&lt;</span> <span class="identifier">State</span> <span class="special">&gt;</span><span class="special">::</span><span class="identifier">operations_type</span></pre>
<p>The operations type. </p>
</li>
<li class="listitem">
<pre class="literallayout"><span class="keyword">typename</span> Resizer <span class="special">=</span> <span class="identifier">initially_resizer</span></pre>
<p>The resizer policy type. </p>
</li>
</ol></div>
</div>
<div class="refsect2">
<a name="idm47870"></a><h3>
<a name="boost.numeric.odeint.runge_kutta4construct-copy-destruct"></a><code class="computeroutput">runge_kutta4</code> 
        public
       construct/copy/destruct</h3>
<div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem">
<pre class="literallayout"><a name="idm29434-bb"></a><span class="identifier">runge_kutta4</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">algebra_type</span> <span class="special">&amp;</span> algebra <span class="special">=</span> <span class="identifier">algebra_type</span><span class="special">(</span><span class="special">)</span><span class="special">)</span><span class="special">;</span></pre>Constructs the <code class="computeroutput"><a class="link" href="runge_kutta4.html" title="Class template runge_kutta4">runge_kutta4</a></code> class. This constructor can be used as a default constructor if the algebra has a default constructor. <p>
</p>
<div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody><tr>
<td><p><span class="term">Parameters:</span></p></td>
<td><div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody><tr>
<td><p><span class="term"><code class="computeroutput">algebra</code></span></p></td>
<td><p>A copy of algebra is made and stored inside explicit_stepper_base. </p></td>
</tr></tbody>
</table></div></td>
</tr></tbody>
</table></div>
</li></ol></div>
</div>
<div class="refsect2">
<a name="idm47903"></a><h3>
<a name="idm29382-bb"></a><code class="computeroutput">runge_kutta4</code> public member functions</h3>
<div class="orderedlist"><ol class="orderedlist" type="1">
<li class="listitem">
<pre class="literallayout"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> System<span class="special">,</span> <span class="keyword">typename</span> StateIn<span class="special">,</span> <span class="keyword">typename</span> DerivIn<span class="special">,</span> 
         <span class="keyword">typename</span> StateOut<span class="special">&gt;</span> 
  <span class="keyword">void</span> <a name="idm29383-bb"></a><span class="identifier">do_step_impl</span><span class="special">(</span><span class="identifier">System</span> system<span class="special">,</span> <span class="keyword">const</span> <span class="identifier">StateIn</span> <span class="special">&amp;</span> in<span class="special">,</span> <span class="keyword">const</span> <span class="identifier">DerivIn</span> <span class="special">&amp;</span> dxdt<span class="special">,</span> 
                    <span class="identifier">time_type</span> t<span class="special">,</span> <span class="identifier">StateOut</span> <span class="special">&amp;</span> out<span class="special">,</span> <span class="identifier">time_type</span> dt<span class="special">)</span><span class="special">;</span></pre>This method performs one step. The derivative <code class="computeroutput">dxdt</code> of <code class="computeroutput">in</code> at the time <code class="computeroutput">t</code> is passed to the method. The result is updated out of place, hence the input is in <code class="computeroutput">in</code> and the output in <code class="computeroutput">out</code>. Access to this step functionality is provided by explicit_stepper_base and <code class="computeroutput">do_step_impl</code> should not be called directly. <p>
</p>
<div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody><tr>
<td><p><span class="term">Parameters:</span></p></td>
<td><div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody>
<tr>
<td><p><span class="term"><code class="computeroutput">dt</code></span></p></td>
<td><p>The step size. </p></td>
</tr>
<tr>
<td><p><span class="term"><code class="computeroutput">dxdt</code></span></p></td>
<td><p>The derivative of x at t. </p></td>
</tr>
<tr>
<td><p><span class="term"><code class="computeroutput">in</code></span></p></td>
<td><p>The state of the ODE which should be solved. in is not modified in this method </p></td>
</tr>
<tr>
<td><p><span class="term"><code class="computeroutput">out</code></span></p></td>
<td><p>The result of the step is written in out. </p></td>
</tr>
<tr>
<td><p><span class="term"><code class="computeroutput">system</code></span></p></td>
<td><p>The system function to solve, hence the r.h.s. of the ODE. It must fulfill the Simple System concept. </p></td>
</tr>
<tr>
<td><p><span class="term"><code class="computeroutput">t</code></span></p></td>
<td><p>The value of the time, at which the step should be performed. </p></td>
</tr>
</tbody>
</table></div></td>
</tr></tbody>
</table></div>
</li>
<li class="listitem">
<pre class="literallayout"><span class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> StateIn<span class="special">&gt;</span> <span class="keyword">void</span> <a name="idm29423-bb"></a><span class="identifier">adjust_size</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">StateIn</span> <span class="special">&amp;</span> x<span class="special">)</span><span class="special">;</span></pre>Adjust the size of all temporaries in the stepper manually. <p>
</p>
<div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody><tr>
<td><p><span class="term">Parameters:</span></p></td>
<td><div class="variablelist"><table border="0" class="variablelist compact">
<colgroup>
<col align="left" valign="top">
<col>
</colgroup>
<tbody><tr>
<td><p><span class="term"><code class="computeroutput">x</code></span></p></td>
<td><p>A state from which the size of the temporaries to be resized is deduced. </p></td>
</tr></tbody>
</table></div></td>
</tr></tbody>
</table></div>
</li>
</ol></div>
</div>
</div>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2009-2015 Karsten Ahnert and Mario Mulansky<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
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